ok i dont really know about the codeing here but you would need the game (or some form of program that would collect the data from the players computers and then send out data to adjust the souroundings apropriatly) to be running on your server all the time. Then each player would need a copy of the game that would run like a single player game but when the player does something that effects another player or the souroundings (eg. dropping a poition)it needs to send that data to the program running on the server. The server then needs to send that data out to all the other players.
ok im not quite sure if thats what you were asking but i hope it helps anyway.
Darkness will claim us all